The search by mankind for absorption of unpleasant aromas and scents in the air that we breathe is as old as civilization. The earliest documents come from the Egyptians that used substances like charcoal, to absorb from the air the scent of the cadavers in the mummification process.
Over the centuries these processes of purification for breathable air evolved in their technique, particularly at the beginning of the XX century due to the advent of toxic gases for military purposes. This evolution consisting in the filtration of breathable air has progressed to satisfy military and industrial necessities. Quick advances in the state of the art where made during the second half of the XX century, to improve the quality of the air in closed spaces, due to the contaminants in the air, generated by industry, transportation and in general by modern human activities. These filtration and purification systems in general are expensive and active in nature, requiring energy to circulate the air for its filtration.
On the other hand the evolution of passive systems has been slow and not as effective as that of the active systems. Passive systems do not require energy to absorb scents; fans or forced air through filters are not necessary to absorb gases or undesirable substances in the air. Passive systems are characterized to be substances or products that exposed to the environment, absorb, adsorb (accumulation on the surface) or react chemically to eliminate undesirable scents, gases or particles from the air.
The necessity to counteract or to eliminate, effectively and economically, the undesirable odors in the air has increased along with population growth, especially in urban concentrations since this is where the largest amount of pollutants and substances that bother human smell are generated. Examples of patents addressing this problem, are U.S. Pat. Nos. 5,944,704; 5,932,495; 5,932,147; 5,891,508; 5,861,147; 5,856,248; 5,807,364; 5,782,409; 5,733,272; 5,714,137 and the U.S. Pat. No. 5,593,670.
Examples common to the necessity of counteracting these polluting agents that cause bad odors are: the elimination of the aroma of tobacco smoke and its smell that impregnates closed spaces, such as houses, offices and automobiles. The malodor of garbage in kitchens, houses and buildings. The necessity to absorb or to neutralize scents during storage of foods, ranging from domestic to commercial and industrial refrigerators. The previous examples are just a small sample of the dynamic and ever more complex universe of human beings and pets, cohabiting and using progressively more consumer goods in continuously reducing spaces.
In the combat of malodor scents, the most common and oldest is the one characterized by the use of substances that contain perfumes to mask scents. The masking of scents is the concealment of one smell by another, usually a malodor. However the preferences for different aromas vary according to the individual and require relatively large amounts of perfume to counteract smelly malodor aromas.
Other forms of controlling malodor are, for example, the use of chemical substances. These processes are known in the state of the art as degradation by oxidation, where oxidizing agents such as: Chlorine bleach, Sodium hypochlorite, Chlorine Dioxide, and Potassium Permanganate are used. Other forms use degradation processes for reduction of malodor, these use active ingredients such as, Sodium Bisulfate to reduce malodor. These substances can be dangerous and aggressive for humans if used in direct form or exposed to the environment, they may also be harmful if in direct contact to cloths and many different surface materials.
Another method for the control of malodor is the use of active ingredients designed to react with smelly or malodor substances, by using specific chemical groups. Examples of these substances are the biguanid polymers that are mingled with organic compounds that contain atoms N and/or S, as well as the esters of fatty alcohol's of Methyl Metacrylic that react with thiols, ammines and aldehydes. Their benefits are limited since they only react with certain very specific types of malodor.
Other types of well-known compounds are deodorants, in the state of the art these are antibacterial and fungicidal which destroy microorganisms that produce malodor. These compounds, typical in formulations of products for personal hygiene, are not effective in combating smelly substances that have already been generated and that do not come from sources like tobacco smoke or food.
Other forms of eliminating undesirable aromas from the air, are achieved, using absorbent substances or products. Malodor particles or compounds stick to their molecular structure; these chemical compositions are the cause of malodor. Other absorbent agents are characterized by admitting and retaining the malodor molecule inside their molecular structure. Among the more common absorbent agents are charcoal, alkaline compounds such as sodium bicarbonate, aluminum silicates and Zeolite. Some chemical substances are also absorbents, such as: Ciclodextrine whose intermolecular cavities admit small molecules of malodor. However, Ciclodextrin, especially when formulated in a watery solution, is considered fertile ground for microorganisms, given their important glucose content.
Finally it is necessary to consider that conceptually there are two forms of achieving reduction or elimination of malodor. The first is called a passive system, meaning that upon exposure to the environment, the active ingredient or the absorbent agent eliminates malodor scents from the surrounding air by contact. The second is an active system that achieves effectiveness by utilizing a mechanical devise. Most common are forced air systems that circulate air that in combination with absorbent or active ingredients, filter, absorb, perfume, or react chemically with malodor substances.